Brake fluid isn't a single, interchangeable product — DOT 3, DOT 4 and DOT 5.1 are all glycol-based fluids with different boiling points and viscosity characteristics, and picking the wrong one can affect braking performance under heavy use.
The key number: boiling point
Brake fluid absorbs moisture from the atmosphere over time (it's hygroscopic by design, so any moisture that gets into the system doesn't pool in one place). As water content rises, the fluid's boiling point drops — and if it boils inside the caliper under heavy braking, you get a spongy pedal or brake fade. That's why every DOT grade specifies both a dry boiling point (fresh fluid) and a wet boiling point (after absorbing a specified amount of moisture).
- DOT 3 — the baseline for most passenger cars, two- and three-wheelers.
- DOT 4 — a higher dry and wet boiling point than DOT 3, using a borate-ester additive package, common on modern passenger cars, SUVs and ABS-equipped vehicles.
- DOT 5.1 — the highest boiling point of the glycol-based grades, formulated for severe-duty and performance braking systems, while remaining compatible with DOT 3/4 systems (unlike silicone-based DOT 5, which is a different chemistry entirely and must never be mixed with these).
Which one do you need?
Always use the grade specified in your vehicle's owner's manual or on the brake fluid reservoir cap. Upgrading from DOT 3 to DOT 4 within the same vehicle is common practice for extra thermal headroom; downgrading is not recommended. Never mix silicone-based DOT 5 fluid into a system designed for glycol-based DOT 3/4/5.1.
AGREX Brake Fluid range
AGREX manufactures DOT 3, DOT 4, Super DOT 4 (low viscosity) and DOT 5.1 brake fluids to IS 8654. See full specifications on our Brake Fluid DOT 3 page and the related grades linked from it, or talk to our team about bulk or OEM supply.